Handling and Surface Modificaiton pf Ultrafine Particles by CVD in Fluidized Bed Under Reduced Pressure

化学气相沉积法在制备化学成分和晶体组成可控的超细颗粒方面具有很大的吸引力。其中最重要的因素之一是如何处理气相中的细小颗粒。本研究采用流态化技术处理超细颗粒：(1)将直径30~400 nm的氮化硅、碳化硅、氧化铝和二氧化钛颗粒在0.1~100kPa25~200ﾟC下进行流态化处理，利用光纤探头和压力传感器对床层不同位置的气泡、夹带和混合特性进行了评价。流态化气体为干燥空气或氮气，气速大于1 cm/S。粘性颗粒也可通过掺入粗颗粒作为湍流促进剂进行流态化。从颗粒的物理化学性质角度对其流态化性能进行了关联。(2)CVD工艺实际是在直径为28 mm的小型流化床中进行的。其中包括用NH3和TiCl4反应在Si_3N_4或Al_2O_3上涂覆导电TiN，用NH_3和AlCl3反应在Al_2O_3上涂覆导热AIN。结果表明，利用CVD反应对超细粒子进行流态化改性是非常有效的。

Chemical vapor deposition method is very attractive to produce ultrafine particles with controlled chemical and crystalline compositions. One of the most important factors is how to handle fine particles in the gas phase. In this study, fluidization, which is normally used only for coarse particles, is refined for the handling of ultrafine particles.(1) Si_3N_4, SiC, Al_2O_3 and TiO_2 particles of 30-400 nm diameter were fluidized under 0.1-100 kPa and 25-200^ﾟC, and characteristics of bubbles, entrainment and mixing were evaluated by using optical fiber probes and pressure sensors equipped at various positions in the bed. The fluidization gas was dry air or nitrogen, and the gas velocity was larger than 1 cm/s. Cohesive particles were also fluidized by mixing coarse particles as the turbulent promoter. The fluidizability was correlated from the view of physicochemical properties of particles.(2) CVD processing were actually carried out in a bench-scale fluidized bed of 28 mm diameter. The coating of Si_3N_4 or Al_2O_3 with electro conductive TiN by the reaction of NH_3 and TiCl_4, and the coating of Al_2O_3 with thermo-conductive AIN by the reaction of NH_3 and AlCl_3 were among them. The results show that the fluidization is very effective to modify ultrafine particles by CVD reactions.